1. Field of the Invention
The present invention relates to a thermal development apparatus and a cooling method therefor, and in particular relates to a dry thermal development apparatus, for performing a heating process using a thermal development sheet that does not require a wet process, and a cooling method therefor.
2. Description of the Related Art
Conventionally, a wet system that develops or records an image on a silver halide photographic photosensitive material and performs a wet process to obtain the image, has been employed for a plate making image recording apparatus that prepares a plate for printing, on an image recording apparatus, such as is used for digital radiography, CT or MRI, that records medical images using a heat-accumulating fluorescent sheet.
Recently, the focus has been on a thermal development apparatus that employs a dry system rather than a wet process. This thermal development apparatus employs a photosensitive and/or thermal sensitive recording material (photo/thermal sensitive recording material) film or a thermal development photosensitive material film (hereinafter referred to as a thermal development sheet). In a thermal development apparatus using the dry system, an exposure unit uses a laser beam to irradiate onto (scan on) a recording material and form a latent image. Such a thermal development unit performs the thermal development process by bringing a thermal development sheet into contact with heating means, uses a cooling unit to cool the thermal development sheet on which the image is formed, and then discharges the sheet to the outside.
Since the dry system requires less time to form an image than does the wet system, and since a problem presented by the waste fluid generated by the wet process is eliminated, it is strongly anticipated that in the future the demand for the use of the dry system will increase.
A conventional thermal development apparatus is disclosed in JP (OPI) 2000-98577, for example, and the thermal development apparatus disclosed in this publication will now be described while referring to FIG. 4.
In a thermal development apparatus 60, a thermal development unit 62 is used to develop a thermal development sheet A1, which thereafter is fed by a pair of feeding rollers 62A and 62B to a cooling unit 63, including a cooling member 65 having a curved face 65A and a linear portion 65B. The thermal development sheet A1 is thus cooled until a development stop temperature is reached, whereafter it is discharged by a pair of discharge rollers 64A and 64B.
At this time, since the speed at which the discharge rollers 64A and 64B convey the thermal development sheet A1 is higher than the speed imparted by the feed rollers 62A and 62B, the thermal development sheet A1 can be forcefully guided along the curved face 65A of the cooling member 65 while the temperature of the sheet A1 is higher than the softening point temperature. Therefore, the rigidity of a thermal development sheet A1 is increased to limit the degree to which it is physically deformed, and thereafter, as the sheet A1 advances along the linear portion 65B of the cooling member 65, its permanent deformation (curling) is prevented.
However, in the thermal development apparatus 60, between the thermal development unit 61 and the cooling unit 63, an area for maintaining the thermal development sheet at a development stop temperature is not clearly defined by partition walls. Therefore, the quality of a developed image will vary due to changes in the external temperature and differences in the temperature characteristics of the thermal development sheet.
In addition, in order to stretch the thermal development sheet A1 and remove creases, the sheet A1 is conveyed while forcefully pressed against the curved face 65A of the cooling member 65. However, when the thermal development sheet A1 is pressed against the curved face 65A at a temperature lower than that of the softening point, vertical creases that parallel the direction in which the thermal development sheet A1 is conveyed will not be removed.
To resolve the abovementioned shortcomings, it is one objective of the present invention to provide a thermal development apparatus for preventing the deterioration of image quality due to a temperature change in a cooling space used for halting development, and for preventing the occurrence of vertical creases in a thermal development sheet and a cooling method therefor.
To achieve the above objective, according to a first aspect of the invention, a thermal development sheet cooling method, for cooling a thermal development sheet that is thermally developed at a predetermined development temperature, comprises:
a first cooling step of employing a rotary member pair, kept at a temperature lower than a development temperature, to sandwich and feed a thermal development sheet that has been developed, and of reducing the temperature of the thermal development sheet to suppress further development progression;
a second cooling step of, following the discharge of the thermal development sheet from the rotary member pair, feeding the thermal development sheet in a non-contact state a predetermined distance through the air at a temperature lower than the temperature of the rotary member pair, thereby cooling the thermal development sheet while the inherent weight thereof induces curling; and
a third cooling step of feeding the thermal development sheet while in contact with a guide member, and of cooling the thermal development sheet to a temperature equal to or lower than a softening point temperature of a sheet support member,
wherein the cooling of the thermal development sheet is accomplished in the first to the third cooling steps.
By the thermal development method, since in the first cooling area, immediately following the thermal development process, the thermal development sheet is sandwiched and fed by the rotary member pair at a predetermined temperature that is lower than the development temperature, the temperature of the thermal development sheet is reduced and further development progression is suppressed. Therefore, since the development time can be rigorously managed, image quality is less affected by changes in the external temperature.
In the second cooling area, since the thermal development sheet in the non-contact state is fed a predetermined distance through the air at a temperature lower than the temperature of the rotary member pair, the thermal development sheet is cooled while its inherent weight induces its curling. Therefore, a thermal development sheet that becomes soft at a temperature higher than the softening point temperature of the sheet support member can be naturally cooled without imposing an external load on the sheet, so that the occurrence of vertical creases in the thermal development sheet can be prevented. Further, the rigidity of a thermal development sheet can be increased when its curling is induced by its inherent weight.
In the third cooling area, a thermal development sheet is fed while in contact with the guide member, and is cooled to a temperature equal to or lower than the softening point temperature of the sheet supporter. Therefore, the curling direction of the thermal development sheet is forcibly altered by winding the curled sheet in the opposite direction, thereby returning the sheet to its original plane shape. Furthermore, additional rigidity is imparted to the thermal development sheet when it is wound in the opposite direction.
According to a second aspect, a thermal development apparatus comprises:
a cooling unit, for cooling a thermal development sheet that is thermally developed at a predetermined development temperature,
wherein the cooling unit includes
a first cooling area, wherein the cooling unit employs a rotary member pair, kept at a temperature lower than a development temperature, to sandwich and feed the thermal development sheet that is developed, and reduces the temperature of the thermal development sheet to suppress further development progression,
a second cooling area, wherein, following the discharge of the thermal development sheet from the rotary member pair, the cooling unit feeds the thermal development sheet in a non-contact state a predetermined distance through the air at a temperature lower than the temperature of the rotary member pair, thereby cooling the thermal development sheet while the inherent weight thereof induces curling,
a third cooling area, wherein a guide member is provided along which the thermal development sheet is sandwiched and fed to correct the curved shape thereof, and wherein the cooling unit cools the thermal development sheet to the temperature of a sheet support member that is equal to or lower than a softening point temperature; and
a fourth cooling area, wherein discharge rollers are provided for sandwiching and for discharging to the outside the thermal development sheet that is fed along the guide member, and wherein the temperature of the thermal development sheet is further reduced.
In the thermal development apparatus, since in the first cooling area, immediately following the thermal development process, the thermal development sheet is sandwiched and fed by the rotary member pair at a predetermined temperature that is lower than the development temperature, the temperature of the thermal development sheet is reduced and further development progression is suppressed. Therefore, since the development time can be rigorously managed, image quality is less affected by changes in the external temperature.
In the second cooling area, since the thermal development sheet in the non-contact state is fed a predetermined distance through the air at a temperature lower than the temperature of the rotary member pair, the thermal development sheet is cooled while its inherent weight induces its curling. Therefore, a thermal development sheet that becomes soft at a temperature higher than the softening point temperature of the sheet support member can be naturally cooled without imposing an external load on the sheet, so that the occurrence of vertical creases in the thermal development sheet can be prevented. Further, the rigidity of a thermal development sheet can be increased when its curling is induced by its inherent weight.
In the third cooling area, a thermal development sheet is fed while in contact with the guide member, and is cooled to a temperature equal to or lower than the softening point temperature of the sheet supporter. Therefore, the thermal development sheet, while contacting the guide member, is gradually cooled to a temperature equal to or lower than the softening point temperature of the sheet support member, while at the same time, the curling direction is forcibly altered by winding the curled sheet in the opposite direction, thereby returning the sheet to its original plane shape. Furthermore, additional rigidity is imparted to the thermal development sheet when it is wound in the opposite direction.
In the fourth cooling area, discharge rollers are provided for sandwiching a thermal development sheet and reducing its temperature, while conveying it along the guide member and then discharging it to the exterior. With this arrangement, once the thermal development sheet has been discharged it is cool enough to be picked up and handled by hand.